Crystalline polypropylene is an excellent material in extensive use which has comparatively good mechanical and thermal characteristics. It is known that mechanical characteristics and thermal characteristics are closely related to the degree of crystallinity, and research to increase the crystallinity of crystalline polypropylene is proceeding.
In general, with the goal of improving mechanical and thermal properties of polypropylene, control of the stereoregularity, molecular weight, and molecular weight distribution (for example, Japanese Patent Application, First Publication, No. 62-195007), the addition of crystal nucleating agents (for example, Japanese Patent Application, First Publication, No. 62-209151), the addition of various filling agents such as fiber (for example, Japanese Patent Application, First Publication, No. 61-160359), the carrying out heat treatments after molding (for example, Japanese Patent Application, First Publication, No. 62-256837), and the like have been attempted. However, when crystalline polypropylenes have been obtained by crystallization under normally used molding conditions, the degree of crystallinity of the polypropylene is not sufficiently increased because the rate of crystallization of the polypropylene is slow.
Polypropylenes are crystalline high polymers, and when crystallized without orientation, spherulites are formed. These spherulites are formed from lath like crystals called lamella, but in situations of polypropylene spherulites of a normal monoclinic crystal (.alpha.-crystal), it is known that they comprise lamellae which extend radiating from the center of the spherulite (herein after referred to as R-lamella) and lamellae which extend at angle of approximately 80 degrees 40 minutes from the R-lamella (hereinafter referred to as T-lamella).
Because of the presence of this type of spherulite structure, it has not been possible to improve the degree of crystallinity and, as a result, it has not been possible to improve rigidity. In addition, because the lamella thickness of the T-lamella is thin compared with the thickness of the R-lamella, the melting point is low and, therefore, the heat distortion temperature is also low.